llvmpipe: Implement manual context resets

Make it possible to trigger a emulated GPU reset by creating a file at
the path of the `LP_CONTEXT_RESET_FILE` env var. All llvmpipe contexts
using the `LOSE_CONTEXT_ON_RESET` strategy that where created before
the that file will start returning `PIPE_UNKNOWN_CONTEXT_RESET` in
`get_device_reset_status()`, while newer contexts - most notably those
created by apps in reaction to the device reset - continue to return
`PIPE_NO_RESET`.

Note that, because we're dealing with files, rtime is used instead of
mtime as the later

Usage:
```
LP_CONTEXT_RESET_FILE=~/llvmpipe_reset LIBGL_ALWAYS_SOFTWARE=1
someapp
touch ~/llvmpipe_reset
```

Signed-off-by: Robert Mader <robert.mader@collabora.com>
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/40681>

docs/envvars.rst

@@ -1356,6 +1356,14 @@ LLVMpipe driver environment variables
    turns off threading completely. The default value is the number of
    CPU cores present.
 
+.. envvar:: LP_CONTEXT_RESET_FILE
+
+   a file path. If set, contexts using the LOSE_CONTEXT_ON_RESET strategy will
+   check it for the presence and modification time of a file and trigger an
+   emulated device reset if they were created before the last modification time.
+
+   Currently not available on Windows.
+
 VMware SVGA driver environment variables
 ----------------------------------------
 

src/gallium/drivers/llvmpipe/lp_context.c

@@ -30,6 +30,8 @@
  *    Keith Whitwell <keithw@vmware.com>
  */
 
+#include <sys/stat.h>
+
 #include "draw/draw_context.h"
 #include "draw/draw_vbuf.h"
 #include "pipe/p_defines.h"
@@ -194,6 +196,45 @@ lp_draw_disk_cache_insert_shader(void *cookie,
 static enum pipe_reset_status
 llvmpipe_get_device_reset_status(struct pipe_context *pipe)
 {
+#if !DETECT_OS_WINDOWS
+   struct llvmpipe_context *llvmpipe = llvmpipe_context(pipe);
+   struct stat st_reset_file;
+   struct timespec ts_now;
+   int64_t now_ns;
+
+   if (!(llvmpipe->flags & PIPE_CONTEXT_LOSE_CONTEXT_ON_RESET) ||
+       llvmpipe->context_reset_file_path == NULL)
+      return PIPE_NO_RESET;
+
+   clock_gettime(CLOCK_REALTIME, &ts_now);
+   now_ns = (int64_t)ts_now.tv_sec * 1000000000LL + ts_now.tv_nsec;
+
+   /*
+    * Only return a *RESET* status for ~0.5 milliseconds. From the spec:
+    *
+    * 5. How should the application react to a reset context event?
+    *
+    * RESOLVED: For this extension, the application is expected to query
+    * the reset status until NO_ERROR is returned. If a reset is encountered,
+    * at least one *RESET* status will be returned. Once NO_ERROR is again
+    * encountered, the application can safely destroy the old context and
+    * create a new one.
+    */
+   if (llvmpipe->context_reset_time_ns > 0)
+      return now_ns - llvmpipe->context_reset_time_ns < 500000 ?
+         PIPE_UNKNOWN_CONTEXT_RESET : PIPE_NO_RESET;
+
+   if (stat(llvmpipe->context_reset_file_path, &st_reset_file) == 0) {
+      int64_t file_mod_time_ns = (int64_t)st_reset_file.st_mtim.tv_sec *
+         1000000000LL + st_reset_file.st_mtim.tv_nsec;
+
+      if (llvmpipe->context_creation_time_ns < file_mod_time_ns) {
+         llvmpipe->context_reset_time_ns = now_ns;
+         return PIPE_UNKNOWN_CONTEXT_RESET;
+      }
+   }
+
+#endif
    return PIPE_NO_RESET;
 }
 
@@ -214,6 +255,20 @@ llvmpipe_create_context(struct pipe_screen *screen, void *priv,
 
    memset(llvmpipe, 0, sizeof *llvmpipe);
 
+   llvmpipe->flags = flags;
+#if !DETECT_OS_WINDOWS
+   llvmpipe->context_reset_file_path =
+      os_get_option_secure("LP_CONTEXT_RESET_FILE");
+   if (llvmpipe->flags & PIPE_CONTEXT_LOSE_CONTEXT_ON_RESET &&
+       llvmpipe->context_reset_file_path != NULL) {
+      struct timespec ts_now;
+
+      clock_gettime(CLOCK_REALTIME, &ts_now);
+      llvmpipe->context_creation_time_ns =
+         (int64_t)ts_now.tv_sec * 1000000000LL + ts_now.tv_nsec;
+   }
+#endif
+
    list_inithead(&llvmpipe->fs_variants_list.list);
 
    list_inithead(&llvmpipe->setup_variants_list.list);

src/gallium/drivers/llvmpipe/lp_context.h

@@ -59,6 +59,9 @@ struct lp_velems_state;
 struct llvmpipe_context {
    struct pipe_context pipe;  /**< base class */
 
+   /** Context creation flags */
+   unsigned flags;
+
    struct list_head list;
    /** Constant state objects */
    const struct pipe_blend_state *blend;
@@ -197,6 +200,10 @@ struct llvmpipe_context {
    int max_global_buffers;
    struct pipe_resource **global_buffers;
 
+   /** Used for context reset emulation, see LP_CONTEXT_RESET_FILE */
+   const char *context_reset_file_path;
+   int64_t context_creation_time_ns;
+   int64_t context_reset_time_ns;
 };